1. Field of the Invention
This invention relates to the detection of defects in food, especially fish for human consumption.
2. Discussion of the Related Art
Currently, parasite detection and removal in fish for human consumption is accomplished through visual inspection and manual removal. Detection is assisted by candling, which involves shining a light through each fillet to enhance the ability to detect embedded parasites. This method, although widely used, has several limitations. First, refraction of light by the fish musculature, especially in thick fillets, makes embedded parasites undetectable. Second, the candling process is extremely difficult to automate. Although advancements have been made, it is impossible for these systems to consistently differentiate parasites from other irregularities in the flesh. Light refraction also limits automated detection systems which utilize optical techniques. Third, worker fatigue and boredom reduces the efficiency of the detection and removal process. In addition, defects such as blood clots, bruises and discoloration also introduce inefficiencies. Consequently, candling techniques are labor-intensive and costly. It has also been found that varying light intensity and wavelength affords insufficient improvement in efficiency and may actually increase costs.
Alternatives to optical methods for detecting parasites in fish flesh have also been investigated. These techniques include ultrasonic, ultraviolet light, X-ray, sonic laser acoustic, and electronic candling. These technologies were initially developed for other applications and extensive modifications and adaptations were required for parasite detection. Application of these techniques have only marginally improved the detection efficiency over that of optical techniques. Deeply imbedded parasites may be detected by some of these procedures; however, the accuracy of detection is still limited due to the problem of pattern recognition. Thus far, no satisfactory alternative to candling has been found.
The physical state of agricultural commodities, and to some extent fishery products, has been measured using their electrical properties. See, for example, the German Offenlegungsschrift DE 3910636, published Nov. 30, 1989. Conduction of electrical energy is used for determining moisture content and to predict cooking characteristics in high-frequency dielectric or microwave heating. The Torry meter for example, uses electrical properties of fish flesh to provide a measure of fish quality. Application of electrical properties is also used extensively in the biomedical field to study the function of nerve and muscle fibers. These applications and studies have shown that DC conductivity is the most sensitive indicator of material parameters.
Nevertheless, because of the variation in size and state of fish samples that are not to be further cut up for the commercial market, it is not immediately apparent how to apply such knowledge to detect a hidden defect, such as a parasite.